Atrial fibrillation (AF) is a common and dangerous irregular heart rhythm that affects between 1 and 1.5 million Americans. Specifically, in AF, the normal electrical impulses that are generated by the sinoatrial node are overwhelmed by disorganized electrical impulses that originate in the atria and pulmonary veins, leading to conduction of irregular impulses to the ventricles that generate the heartbeat. To control disorganized electrical impulses, various ablation procedures are currently in use.
Pulmonary venous isolation (PVI) remains the therapy of choice for most AF ablation procedures. It is successful in preventing recurrence of paroxysmal AF in 60-80% of subjects undergoing PVI after a single procedure. In ablation of persistent AF, PVI is typically the first step in a stepwise approach to terminate AF.
Pulmonary vein (PV) isolation using a radiofrequency catheter is the most widespread technique for AF ablation currently. Unfortunately, these procedures are difficult and time consuming, because they require precise catheter manipulation and multiple radiofrequency applications.
An ablation technology that can deliver circumferential antral ablation centered on the PV ostia may facilitate AF ablation. Although a range of different ablation energy sources (e.g., radiofrequency energy and cryotherapy) are available, cryotherapy offers a theoretical advantage in that it does not disrupt target tissue architecture and can reduce complications such as PV stenosis and atrio-oesphageal fistulation. One such device was an ultrasound balloon ablation catheter that delivered energy in a radial fashion at the level of the diameter of the balloon, hence necessitating that the balloon catheter to be placed within the PV when delivering energy. This balloon design was suboptimal because the level of electrical isolation typically excluded the proximal portions of the vein, so PV triggers of AF located at this region would not be included in the ablation lesion. Also, from a safety perspective, the intravenous location of the energy delivery resulted in PV stenosis.
Currently, there are 3 major balloon-based ablation devices at various stages of clinical evaluation: (1) cryoballoon ablation, (2) endoscopic laser ablation, and (3) high-intensity focused ultrasound (HIFU). Each of these has been designed to be placed at the PV ostia so as to theoretically isolate the veins outside their tubular portion.
The three balloon ablation catheter designs are all capable of electrically isolating the PVs outside the tubular portions of the PVs at the level of the PV ostia, and the PV antra are largely left unaffected by this ablation procedure. The importance of PV isolation during catheters ablation of paroxysmal AF has been established by the initial description that the PVs harbor foci that initiate AF, and that in individuals with paroxysmal AF ablation of these foci may eliminate AF. However, direct targeting of these foci fell out of favor for 2 reasons: (1) it was difficult and time consuming to evoke these PV triggers during any given procedure, so it was common to see clinical recurrences from a different focus either within the same PV or from another PV, and (2) excessive ablation within the veins caused PV stenosis. This initial approach was followed by a strategy of routine electrical isolation of all PVs in a given patient.
Although this current approach to ablation of paroxysmal AF has a good efficacy and acceptable safety profile, it remains a technically difficult procedure requiring skilled operators. This has prompted the intense development of catheter systems to rapidly and safely isolate the PVs. But this has not proven to be an easily tractable problem because of the complexity of the PV anatomy. The variability in both PV shape and anatomy is well established. Instead of round PVs that join the LA chamber in a perfectly orthogonal manner, the PVs have an oval configuration and typically have an oblique angle with which they join the LA. In addition, the junction of the PVs with the LA is not distinct and often includes an antrum that may include a large portion of the posterior LA. In fact, some investigators contend that the complete posterior LA must be ablated or otherwise electrically excluded to achieve the best clinical outcome.
Despite current and evolving technologies to provide AF ablation, there is still a need for a technology that can provide ablation in a single step in a precise ring area to avoid the entrance of the pulmonary veins and stenosis. Ideally, this can be accomplished without occlusion of the pulmonary vein circulation to avoid blood stagnation and possible pulmonary infarction and or possibility of cloth and embolous formation. The present disclosure addresses these and other issues as outlined below.